I'm big on subtle hints, and hoping people know a lot about the subject at hand already, because I hate explaining myself.
Eirin is a medical genius, whatever she makes can't really be deadly unless it was intended to be, or at least has some sort of extreme curing ability, such as stopping profuse vomiting. The amount of pills that Alice would have had to take to destroy herself would be akin to just choking on anything, really. The worst that would probably happen is that she would get brain damage from over-activity in the night, which wouldn't kill her, but leave her worse off. The pills were kinda just thrown in there to link this to cannon, as well as give Alice more depression.
Reimu IS a self centered jerk, honestly, and if you were to think about it, Marisa and Reimu fight a LOT. They're friends, sure, but Reimu gets mad at Marisa's shenanigans almost daily, and that could only lead to strife. Their relationship would be akin to loving a bipolar person - They're good one minute, and bitching you out the next. Marisa isn't the kind of person that would put up with somebody who is honestly mad at them every other day, not just a Tsundere mad in which the anger goes away quickly with the right amount of apologizing and/or love. I personally don't see Reimu as being big on the whole love-love thing, she's too concerned with other matters to deal with that kind of thing. Realize that she takes incidents very seriously compared to Marisa, and is probably extremely stressed all the time, always wary of who or what could betray her and Gensokyo next.
You also have to remember that this is Alice's diary, and therefore it's Alice's thoughts. That doesn't mean that everything that is written here is complete fact - it's actually quite skewed, most likely. What REALLY happens in a day is kind of up to the reader, but I guess I could make up a better back story if people REALLY want it. But the point of explaining this is to show how Alice is not thinking rationally. Put it this way: If you were as depressed as Alice for such a long period of time, and it got worse and worse every day, how long could you keep your sanity?
I personally don't think the ending was rushed - Alice's fit of depression started on entry 81, almost 3 months before the ending. Entry 117, which is 52 days before the end, only complicated things. It hit her harder in Entry 137, 32 days before the end. So for 52 days, she just slipped farther and farther down the hole, after subconsciously slipping for 36 days beforehand. That's nearly 3 months of constant and utter rage, depression, confusion, and whatnot. The only *rushed* part about it is how Alice decided to stop writing about things a few days before she decided to follow through with her plans of suicide, thus making the story look shorter, but in reality, it took her about a week. If you look at each post I made as a different "chapter", then maybe it's slightly rushed, but really it's one timeline, and the eventual outcome was setting itsself up since Marisa told her that she doesn't love her.
As for Marisa coming in at -just- the right moment, stories are great like that. This is Gensokyo - blame it on fate, magic, whatever.
I feel like an english teacher. >> (Also, this post isn't to say "screw you" to anybody who commented on the ending feeling rushed, it was to clarify things. I thank you all for reading this, and if enough begging ensues, I was kinda serious about writing a less Alice-biased timeline. (Of course, it would be much shorter, and only focus on key events.))
